Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$127.55	13.298%	$144.5116	$144.51	$144.50	$144.50
Purchase #2	$218.82	13.708%	$248.8158	$248.82	$248.80	$248.80
Purchase #3	$6.74	13.192%	$7.6291	$7.63	$7.65	$7.60
Purchase #4	$90.78	11.441%	$101.1661	$101.17	$101.15	$101.20
Purchase #5	$98.46	6.689%	$105.046	$105.05	$105.05	$105.00
Purchase #6	$149.78	7.649%	$161.2367	$161.24	$161.25	$161.20
Purchase #7	$36.68	10.782%	$40.6348	$40.63	$40.65	$40.60
7 purchase totals =	$728.81		$809.0401	$809.05	$809.05	$808.90